1. Field of the Invention
The present invention relates to a liquid injection device and an inkjet recording device including the same, and more specifically, to a control technology for liquid injection using a so-called multi-dot system.
2. Description of the Related Art
A liquid injection device used for an inkjet recording device or the like includes a liquid injection head injecting a liquid drop and a control device controlling the liquid injection head. For example, an ink injection head in an inkjet recording device includes a pressure chamber temporarily storing ink, an actuator that is in contact with the pressure chamber and includes a piezoelectric element, and a nozzle that is in communication with the pressure chamber and injects an ink drop toward a recording medium such as a recording paper sheet or the like. Such an inkjet recording device is operated as follows. When a driving pulse is transmitted to the actuator, the piezoelectric element is contracted or extended based on the driving pulse. As a result, the interior of the pressure chamber is expanded or contracted to inject ink in the pressure chamber from the nozzle. The injected ink drop lands on the recording medium, and thus one dot (drop corresponding to one pixel) is formed on the recording medium.
In such an inkjet recording device, there is a limit on the amount of liquid contained in one liquid drop that can be stably injected by one driving pulse. Thus, various studies have been made conventionally in order to realize gray scale printing. For example, Japanese Laid-Open Patent Publication No. Hei 10-81012 discloses a method for driving an ink injection head by which the size of dots is adjusted by a multi-dot system. By the multi-dot system, a driving signal including a plurality of driving pulses in one liquid drop injection period for forming one dot is generated. From the plurality of driving pulses, one or at least two driving pulses are selected in accordance with the size of the dot, and are supplied to the actuator driving the ink injection head. For example, for forming a relatively large dot, a first ink drop and a second ink drop are injected in a time-series manner in one liquid drop injection period. Before landing on the recording medium, the first ink drop and the second ink drop are merged.
However, in the ink injection device having the above-described structure, after the second ink drop (main drop) is injected from the nozzle, a satellite leading to a meniscus that forms an ink surface in the nozzle may be generated from the main drop. If being separated from the main drop, the satellite may jump as a satellite drop and land at a position away from the main drop on the recording medium. In the case of moving slowly, the satellite drop may lose a kinetic energy thereof by the influence of the air flow or the resistance of the air, and may become ink mist (microscopic ink drops floating in a disorderly manner) to stain the inside of the recording device or the recording medium. The satellite drop or the ink mist is easily generated in the case where, for example, a printing gap is enlarged in order to inject a large liquid drop or the driving frequency is increased in order to print at a high speed. Therefore, in the case where the printing gap is to be enlarged or the throughput is to be increased, it is desired to more effectively suppress or prevent the long satellite drop or the ink mist.